In the case of a positive Trendelenburg's sign, which muscle is typically weakened?

• A. Gluteus maximus
• B. Gluteus minimus
• C. Gluteus medius
• D. Sartorius

Answer: (C)

A positive Trendelenburg's sign indicates weakness in the hip muscles responsible for stabilizing the pelvis during the single-leg stance. The specific muscle that is typically weakened in this case is the gluteus medius. This muscle is crucial for abducting the thigh and supporting the pelvis when standing on one leg. When the gluteus medius is weak, the pelvis cannot be properly stabilized, leading to a drop on the opposite side when the patient stands on one leg, hence a positive Trendelenburg's sign.

The gluteus maximus primarily functions in hip extension and has a less direct role in stabilizing the pelvis during the stance phase of walking or standing on one leg. Similarly, while the sartorius is involved in hip flexion and abduction, it does not play a significant role in maintaining pelvic stability in the same way that the gluteus medius does. Therefore, recognizing the pivotal role of the gluteus medius in maintaining pelvic alignment is key to understanding the implications of a positive Trendelenburg's sign.